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Get the reporting, research and analysis behind on-air stories straight from the CNN Medical Unit, led by chief medical correspondent Dr. Sanjay Gupta.

Can an eye exam detect multiple sclerosis?

• A five-minute eye exam may be an effective way to detect multiple sclerosis • The exam usually costs only around $75 per eye • An expensive MRI brain image is the current standard test used to detect MS

Bottom Line: If findings hold up, the eye exam could be used more often to identify and monitor multiple sclerosis

Overview

A five-minute eye exam costing about $150 for both eyes might prove to be an inexpensive and effective way to gauge and track the neurological disease multiple sclerosis, potentially complementing costly magnetic resonance imaging to detect brain shrinkage, a characteristic of the disease's progression. The current standard is MRI testing, which takes at least an hour and costs about $1,200. The research was done at Johns Hopkins University and was published in the October 16, 2007, issue of the journal Neurology.

Questions and answers

What does the eye have to do with MS, a disease of the brain and spinal cord?

Dr. Sanjay Gupta, CNN chief medical correspondent: The optic nerve, which is behind the eye, is actually part of the brain. In fact, it's the only part of the brain you can see from the outside. A common early warning sign that you may have MS is vision problems that originate in the optic nerve. So a damaged optic nerve becomes a perfect place to look for early MS.

Gupta: Usually, to test for MS, doctors would use an MRI. The problem with MRI for multiple sclerosis is that it's a limited test. It can see inflammation in the brain, but not nerve damage. So this test is exciting in that it may tell us something we've never been able to see with MS: that nerve damage. The machine used to test the optic nerve is called an "optical coherence tomography," or OCT. This OCT machine acts like a huge microscope for the eye. This machine is also used to test for glaucoma.

One exciting thing, say study authors, is how inexpensive this new way of testing will be if it pans out. It costs $150 for an exam using this OCT method, as opposed to $1,200 for an MRI. The MRI takes an hour. This exam would take five minutes.

When will this test be available?

Gupta: If it becomes something used more often -- and the soonest that could happen is in a few years -- it would be used only if a patient has already experienced some of the other early warning signs of multiple sclerosis. Those signs happen in people between 20 and 50 who experience one or more symptoms such as blurred vision, fatigue, heat sensitivity, depression, numbness and bladder problems. If a person did have these symptoms, and his eye exam proved he had early MS, then he would be put on an approved MS drug.

-- potential to track the disease at a fraction of the cost of current test

A five-minute eye exam might prove to be an inexpensive and effective way to gauge and track the debilitating neurological disease multiple sclerosis, potentially complementing costly magnetic resonance imaging to detect brain shrinkage - a characteristic of the disease's progression.

A Johns Hopkins-based study of a group of 40 multiple sclerosis (MS) patients used a process called optical coherence tomography (OCT) to scan the layers of nerve fibers of the retina in the back of the eye, which become the optic nerve. The process, which uses a desktop machine similar to a slit-lamp, is simple and painless. The retinal nerve fiber layer is the one part of the brain where nerve cells are not covered with the fat and protein sheathing called myelin, making this assessment specific for nerve damage as opposed to brain MRI changes, which reflect an array of different types of tissue processes in the brain.

Results of the scans were calibrated using accepted norms for retinal fiber thickness and then compared to an MRI of each of the patient's brains - also calibrated using accepted norms. Experimenters found a correlation coefficient of 0.46, after accounting for age differences. Correlation coefficients represent how closely two variables are related -- in this case MRI of the brain and OCT scans. Correlation coefficients range from -1 (a perfect opposing correlation) through 0 (no correlation) to +1 (a perfect positive correlation). In a subset of patients with relapsing remitting MS, the most common form of the disease, the correlation coefficient jumped to 0.69, suggesting an even stronger association between the retinal measurement and brain atrophy.

"This is an encouraging result," says Johns Hopkins neurologist Peter Calabresi, M.D., lead author of the study, which appears in the October 2007 issue of Neurology. "MRI is an imperfect tool that measures the result of many types of tissue loss rather than specifically nerve damage itself. With OCT we can see exactly how healthy these nerves are, potentially in advance of other symptoms."

In addition, says Calabresi, OCT scans take roughly one-tenth as long and cost one-tenth as much as the MRI, which means they are faster and cheaper to use in studies that track the effectiveness of new treatments for MS.

Approximately 400,000 people in the United States have MS, marked by an abnormal immune system that attacks and kills a person's own brain cells. As these neurons die, the volume of the brain decreases. MRI of the brain, which can measure total volume, has long been the primary tool used to monitor MS. But MRI, aside from being expensive and uncomfortable, is often misleading since brain inflammation - also a symptom of the disease - can skew brain volume readings. Also, the brain begins shrinking relatively late in the progression of the disease, so MRI isn't as good at detecting the disease in its early stages when treatments are most effective. OCT scans look directly at the thickness, and therefore health, of the optic nerve, which is affected early on in the disease, often before the patient suffers permanent brain damage.

Calabresi added that many of the disabilities suffered by MS patients - numbness, tingling, visual impairment, fatigue, weakness and bladder function disturbance - are the result of nerve cell degeneration, so a test that specifically measures nerve cell health is potentially the clearest picture of the status of the disease.

He cautions that optic nerve damage can point to a number of diseases and is not a unique diagnostic tool for MS. However, he says, it certainly sends up a flag suggesting that MS might be present. And since optic nerve damage is one of the first recognizable symptoms of MS, doctors have a chance to identify the disease potentially before the patient suffers the physical limitations generally associated with its advanced stages.

"Treatments for MS cannot reverse the damage but they can arrest it, so the earlier we get someone on medication the quicker we can stop the disease from causing more harm," says Calabresi. This tool may be useful as an outcome measure in MS clinical trials to assess the efficacy of neuroprotective drugs.

In the study, researchers recruited 40 patients from the Johns Hopkins MS clinic. Twenty had relapsing remitting MS, 15 had secondary progressive MS, and five had primary progressive MS. Researchers also recruited 15 healthy control patients free from ophthalmological or neurological disease as a comparison group.

Calabresi says his next step will be to look at changes in the fiber layer thickness in 100 patients over a period of three years.

Additional researchers who worked on this study from Johns Hopkins include Eliza Gordon-Lipkin, B.S., of the Department of Neurology, and Daniel S Reich, Ph.D., M.D., of the Department of Radiology; Seth A Smith, Ph.D., and BettyAnn Chodkowski, M.S., of the Department of Functional MRI, Kennedy Krieger Institute; and Mathew Pulicken, M.B.B.S., M.H.S., of the Bloomberg School of Public Health. Elliot M Frohman, M.D., Ph.D., of the Department of Neurology, University of Texas, Dallas; Gary Cutter, Ph.D., of the School of Public Health Department of Biostatistics, University of Alabama; and Laura Balcer, M.D. of the Department of Neurology, University of Pennsylvania, also contributed to this study.

The information contained on this page does not and is not intended to convey medical advice. CNN is not responsible for any actions or inaction on your part based on the information that is presented here. Please consult a physician or medical professional for personal medical advice or treatment.